Priority is claimed with respect to application No. 99810832.8 filed on Sep. 17, 1999, in the European Patent Office, the disclosure of which is incorporated herein by reference.
The invention relates to a glue applicator for applying an adhesive to the back or bordering regions of an inner book guided past the applicator, comprising a trough that holds the adhesive, into which at least one applicator roller that transfers the adhesive onto the back of the inner book protrudes, the roller being driven in the same direction as the inner book and, after the approach region to the inner book, forming a break-off region for the adhesive with the approach region.
A glue applicator of the above-described type is schematically outlined in, for example, xe2x80x9cIndustrielle Buchbinderei [Industrial Bookbinding]xe2x80x9d by Dieter Liebau, 1997, Beruf+Schule Itzehoe [publisher]. This glue applicator has two applicator rollers, which are disposed one behind the other and transfer the adhesive from a trough onto the back of an inner book twice.
The selected metering of the adhesive to be transferred is effected by a doctor blade disposed upstream of the application region. A spinner that rotates in the opposite direction of the conveying direction of the inner book, and often at a higher rotational speed than the applicator roller associated with it, levels the adhesive layer applied to the back of the inner book. The rotational speed of an applicator roller approximately corresponds to the transport speed of the inner books.
The adhesive taken up from the trough by an applicator roller is applied to a specific layer thickness by a doctor blade prior to the transfer to the back of the inner book, then applied to the back of a co-rotating inner book. In terms of a favorable penetration by the adhesive, the established distance between the back of the inner book and the surface of the applicator roller generates a specific penetration pressure on the adhesive to be transferred; this pressure is alleviated again after the closest approach, with an uneven layer of adhesive being left behind on the back of the inner book. The spinner levels the uneven area left on the back of the inner book by removing so-called glue threads from the adhesive.
The position of the adhesive break-off region depends on, among other things, the viscosity of the adhesive, the distance between the back of the inner book and the applicator roller, the thickness of the adhesive to be applied, the running speed and the roller diameter. In addition to being inadequate, the adhesive surface is thicker in the longitudinal center than at the edges due to the surface tension of the adhesive. Consequently, the desired application thickness for an optimum binding quality often cannot be achieved in the edge regions. The shearing stress of the adhesive, as created by the spinner, often leads to uncontrollable penetration at the side edges of the back of the inner book, or to diminished quality.
It is therefore an object of the invention to embody a glue applicator of the type mentioned at the outset such that simple means eliminate the aforementioned disadvantages.
The above and other objects are achieved according to the invention by the provision of an applicator for applying an adhesive to a spine or adjoining regions of a book block conveyed guided past the applicator along a conveying plane in a conveying direction, comprising: a trough for holding the adhesive; at least one applicator roller protruding into the trough and arranged for transferring adhesive onto the spine of the book block for forming an adhesive layer on the spine, the roller being driven in a direction which is the same as the conveying direction and defining an approach region in which the surface of the roller approaches the conveying plane; and a sharply-pointed separating wedge disposed downstream of the approach region of the applicator roller and forming a separating region for the supplied adhesive between the applicator roller and the conveying plane of the book block.
By so disposing the sharply-pointed separating wedge, a flowing, longitudinal separation of the supplied adhesive layer is possible after the adhesive has been transferred onto the spine of the book block.
The separating wedge is advantageously adjustable for changing its position, so it can be adapted to variable application conditions.
The wedge surface of the separating wedge that faces the conveying plane of the back of the inner book preferably forms an acute xe2x80x9chold-offxe2x80x9d angle with the conveying plane, which opens in the conveying direction, thereby effecting a clean separation between the adhesive applied to the spine of the book block and the separating wedge.
For further treating the surface of the adhesive layer applied to the spine of the book block, a smoothing apparatus, which scrapes the surface of the adhesive, is provided downstream of the separating wedge. This smoothing apparatus advantageously has a level surface that faces the conveying plane of the book block and can be positioned to contact the applied adhesive at a substantially flat angle, so that the adhesive can be easily removed or leveled.
The apparatus of the invention is described below by way of an embodiment, with reference to the drawing, which includes all of the details that are not mentioned in the description.